The present invention relates to an actuator arrangement for a clutch of a drive train for motor vehicles, which clutch is prestressed into an opened position and can be activated electromechanically, having an electric motor which can be coupled to the clutch in order to activate it, and having a control unit for actuating the electric motor.
Clutches for motor vehicles are available in different designs. Nowadays, the prior art comprises dry clutches which are opened by pressing a clutch pedal. Without activation, these clutches are normally closed. New clutch systems in double clutch gear mechanisms have now become available on the market.
These double clutches are frequently activated hydraulically and are generally normally open, i.e. without activation the clutch opens. This has the advantage that in the event of a fault (for example when there is a loss of pressure) both clutches open and a safe state is therefore assumed. In this context it is sufficient to allow only a small quantity of pressurized oil to escape from the hydraulic activation cylinders of the double clutches in order to eliminate the pressure completely, i.e. as far as the kiss point of the clutch. This occurs very quickly with hydraulic clutches. Even when there is a serious fault (for example processor fault, etc.) in the case of a reset, the two clutches open sufficiently quickly in order to bring about the safe state. In the case of a reset, all the outputs of the control unit (SG) are switched off in a controlled fashion and the control unit is subsequently rebooted.
Closing the two clutches simultaneously with gear speeds engaged in both component gearboxes could lead to a stressed state in the gearbox, with the risk of the drive axle becoming locked.
Furthermore, clutch systems according to the normally stay (or normally hold) principle are also known. In these actuator arrangements, the respective clutch is held in the current state.
In the case of double clutch gear mechanisms, as well as hydraulically activated systems increasing emphasis is being put on electromechanically activated systems. The reasons for this are lower complexity, an advantage in terms of consumption (less energy required for activating the clutch) and lower costs. However, these systems have, due to the system, slight deficits in the field of dynamics. Such electromechanically activated double clutches (that is to say clutches activated by electric motors or solenoids etc.) achieve sufficiently good actuation times when activated actively by the electric motors, with the result that the safe state can be brought about by actively opening the clutches.
These clutches have also preferably been embodied in the past as normally open systems (for the same reasons as above: a safe state is brought about automatically). The restoring force for opening the clutches is produced here by means of a spring. In the case of a reset, the springs must therefore open the two clutches, and at the same time the two electric motors and the coupling elements between the electric motors and the clutches must also be accelerated. This creates problems owing to the considerable moment of mass inertia of the electric motors and the high transmission ratio between the clutches and the electric motors. Furthermore, a very strong restoring spring has to be installed, which gives rise to costs and problems in terms of installation space, and leads to high activation forces when the clutches are closed. As a result, the reductions in consumption which are hoped for in the case of electromechanical actuator arrangements are at least diminished. The loading on the on-board power system of the vehicle increases, due to the high currents of the electric motors, to a high, or even unacceptable, degree.
When a fault state occurs, it may therefore be difficult to open the clutches within the necessary short time in order to bring about the safe state in good time.
Document US 2006/0223672 A1 discloses an automated change-speed gear mechanism whose clutch actuator has at least two electric motors for actuating the clutch. If one of the electric motors fails, this can be sensed. The clutch is a normally closed clutch.
In addition, document DE 101 38 395 A1 discloses an emergency activation device for a hydraulically activated clutch which is also embodied as normally closed.
In this context, in order to perform emergency opening of the clutch in the case of a fault, a pressure accumulator is provided by means of which the clutch can be reliably transferred from the normally closed state into an opened state even when the fault state occurs.
A double clutch gear mechanism with electromechanical activation is known from DE 699 22 025 T2.